The struct embedding gives a great deal of power. You can effectively inherit data and methods. And override methods.

I think the only case where classical polymorphism falls down is having to explicitly reference the embedded type in non-method calls. Method calls proxy just fine though.

I get that this isn’t “really” an is-a relationship, but it feels close enough to get work done for me.

package main

type A struct {
    Name string
}

type B struct {
    A
}

func who(a A) {
    println("I am", a.Name)
}

func (a A) whoMethod() {
    println("As a method, I am", a.Name)
}

func (a A) Shout() {
    println("I AM", a.Name)
}

func (b B) Shout() {
    // We also have access to the embedded type's implementation if we want it
    // via b.A.Shout
    println("I SHOUT MY NAME", b.Name)
}

func main() {
    a := A{"alice"}
    b := B{A{"bob"}}

    a.whoMethod()
    b.whoMethod() // Calls the inherited method
    a.Shout()
    b.Shout() // Calls the overridden method
    who(a)
    who(b.A) // who(b) will fail with a compile-time error
}